Field of the Invention
The present disclosure relates to a semiconductor device, and more particularly, to a light-emitting diode and a method of fabricating the same.
Description of the Related Art
In recent years, incandescent lamps and fluorescent lamps have been being replaced with solid-state lightings (SSLs) using light-emitting diodes (LEDs), organic light-emitting diodes (OLEDs), or polymer light-emitting diodes (PLEDs). To this end, direct-bandgap semiconductors in which a momentum at which the energy of the valence band is maximized is identical to a momentum at which the energy level of the conduction band is minimized are considered as candidates for the SSLs. Among the candidates for LED application, zinc oxide is being spotlighted due to various advantages, for example, a direct bandgap with an exciton binding energy of about 60 meV or higher and wide bandgap (about 3.37 eV), morphological diversity, and low cost fabrication.
However, the zinc oxide may be difficult to implement P-type conductivity and realize PN homojunction with the zinc oxide due to its inherent donor defects. As a result, LEDs based on heterojunctions in which N-type zinc oxide has a junction with other P-type material (e.g., p-GaN, p-Si, and P-type organic materials) prevail over that based on homojunction of zinc oxide.
However, LEDs of the homojunction with an epitaxial interface are generally preferred due to better light-emitting efficiency and lower power consumption than LEDs implemented with the heterojunction. The reason thereof is that a homojunction device including same materials having the P-type conductivity and N-type conductivity and having a consistent crystal lattice may preserve lattice periodicity at the interface. On the contrary, a heterojunction device may cause lattice mismatch at the interface between materials constituting the heterojunction. The lattice mismatch causes problems including interfacial defects and strains which deteriorate performance of the device.
Furthermore, most PN junction devices are fabricated in vacuum processes requiring a high temperature (e.g., 500° C. or higher). The high-temperature vacuum processes facilitate mixing of a dopant into a crystal lattice, but may cause the interface to have unclear homojunction due to inter-diffusion of the dopant. Furthermore, a flexible substrate cannot be utilized in a high temperature processes. In other words, the use of PN junction elements in the flexible device may be limited. Furthermore, high costs may be required for fabricating a LED in vacuum processes, and it may be difficult to increase size of the LED due to the physical limitations of equipment related to the vacuum processes.